Srivastava A, Jones E W
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Genetics. 1998 Jan;148(1):85-98. doi: 10.1093/genetics/148.1.85.
The PEP12 homolog Pth1p (Pep twelve homolog 1) is predicted to be similar in size to Pep12p, the endosomal syntaxin homolog that mediates docking of Golgi-derived transport vesicles and, like other members of the syntaxin family, is predicted to be a cytoplasmically oriented, integral membrane protein with a C-terminal transmembrane domain. Kinetic analyses indicate that deltapth1/vam3 mutants fail to process the soluble vacuolar hydrolase precursors and that PrA, PrB and most of CpY accumulate within the cell in their Golgi-modified P2 precursor forms. This is in contrast to a pep12 mutant in which P2CpY is secreted from the cell. Furthermore, pep12 is epistatic to pth1/vam3 with respect to the CpY secretion phenotype. Alkaline phosphatase, a vacuolar membrane hydrolase, accumulates in its precursor form in the deltapth1/vam3 mutant. Maturation of pro-aminopeptidase I, a hydrolase precursor delivered directly to the vacuole from the cytoplasm, is also blocked in the deltapth1/vam3 mutant. Subcellular fractionation localizes Pth1/Vam3p to vacuolar membranes. Based on these data, we propose that Pth1/Vam3p is the vacuolar syntaxin/t-SNARE homolog that participates in docking of transport vesicles at the vacuolar membrane and that the function of Pth1/Vam3p impinges on at least three routes of protein delivery to the yeast vacuole.
PEP12同源物Pth1p（Pep twelve homolog 1）预计大小与Pep12p相似，Pep12p是一种内体Syntaxin同源物，介导高尔基体衍生的运输囊泡的对接，并且与Syntaxin家族的其他成员一样，预计是一种面向细胞质的整合膜蛋白，具有C端跨膜结构域。动力学分析表明，deltapth1/vam3突变体无法加工可溶性液泡水解酶前体，并且PrA、PrB和大部分CpY以其高尔基体修饰的P2前体形式在细胞内积累。这与pep12突变体相反，在pep12突变体中，P2CpY从细胞中分泌出来。此外，就CpY分泌表型而言，pep12对pth1/vam3是上位性的。碱性磷酸酶是一种液泡膜水解酶，在deltapth1/vam3突变体中以前体形式积累。前氨肽酶I（一种从细胞质直接输送到液泡的水解酶前体）的成熟在deltapth1/vam3突变体中也被阻断。亚细胞分级分离将Pth1/Vam3p定位到液泡膜上。基于这些数据，我们提出Pth1/Vam3p是液泡Syntaxin/t-SNARE同源物，参与运输囊泡在液泡膜上的对接，并且Pth1/Vam3p的功能至少影响蛋白质输送到酵母液泡的三条途径。
